|Publication number||US7885137 B2|
|Application number||US 11/967,135|
|Publication date||Feb 8, 2011|
|Filing date||Dec 29, 2007|
|Priority date||Apr 24, 2007|
|Also published as||CN101295542A, CN101295542B, DE102008011514A1, DE102008011514B4, US20080270679|
|Publication number||11967135, 967135, US 7885137 B2, US 7885137B2, US-B2-7885137, US7885137 B2, US7885137B2|
|Original Assignee||Hynix Semiconductor Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Referenced by (4), Classifications (14), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present application claims priority to Korean patent application number 10-2007-0039715, filed on Apr. 24, 2007, which is incorporated by reference in its entirety.
The present invention relates to a flash memory device, and more particularly to a control circuit of a flash memory having a data area and a file allocation table (FAT) area, and a method of operating the flash memory device.
In flash memory devices, an erase/write (E/W) cycling characteristic is an important factor in reliability. The E/W cycling characteristic is used in determining a physical limitation in the number of erase operations and program operations of a flash memory device. This physical limitation is further increased with higher densities of a flash memory device. Recently, a multi-level cell (MLC) technology has been proposed. In the MLC technology, a cell state is divided into more than two states and 2 or more bits of data can be stored in a single cell. However, as the MLC technology is applied to the flash memory devices, the limitation in the E/W cycles becomes more serious.
The localized E/W cycling stress can be reduced by appropriately allocating locations where data are to be written. That is, if data are sequentially written, the E/W cycling stress is concentrated on a previous block. The E/W cycling stress at a specific location can be reduced by writing data at several locations in a uniform manner. This method can reduce the concentration of the E/W stress at the specific block. Hence, the E/W cycling limitation problem that most blocks encounter can be solved to some degree.
The above-described method is effective in the data area but ineffective in the FAT area. The data area refers to a memory area where data are stored, and the FAT area refers to a memory area where information such as location of data within the data area are stored. Therefore, an erase operation is performed on the data area only when new data are written. On the other hand, a data update operation must be performed on the FAT area whenever a data state in the data area is changed. Therefore, the FAT area is more vulnerable to the E/W cycling stress than the data area.
The vulnerability to the E/W cycling stress in the FAT area becomes more serious when operation schemes are different. In the flash memory device, a program operation is performed on a page basis, while an erase operation is performed on a block basis. A plurality of pages define one block. In the data area, an erased state is indicated by “1”, which means that a current flows because the erased state has a negative threshold voltage. A programmed state is indicated by “0”, which means that no current flows because the programmed state has a positive threshold voltage. That is, the state of “1” represents that no data is written. Therefore, in the case of the data area, an additional program has only to be performed on a page basis whenever new data are added. On the other hand, the convention for the FAT area is opposite to that of the data area because of compatibility with other systems, e.g., an operating system. That is, an erased state is indicated by “0” and the programmed state is indicated by “1”. Therefore, when some data are added, an erase operation is performed to change some regions of the FAT area from the “0” state to the “1” state. However, since the erase operation is performed on a block basis, it is impossible to perform the erase operation on only the needed regions. That is, the erase operation is performed over the FAT area and the program operation is then performed to update data.
For these reasons, the E/W cycling characteristic tends to be more important in the FAT area than in the data area. As illustrated in
In one embodiment, there is provided a method of operating a flash memory device having a first area and a second area, a programmed state and an erased state of the first area being opposite to that of the second area. The method includes: receiving a program command; inverting the program data when the received program command is a command for programming the second area; and programming the inverted program data into the second area.
In another embodiment, there is provided a control circuit of a flash memory device including a cell array having a first area and a second area, a programmed state and an erased state of the first area being opposite to those of the second area. The control circuit includes: a flag cell; a flag cell page buffer configured to control an operation of the flag cell; a main page buffer configured to control an operation of the cell array; and a data inverter configured to invert data inputted to the main page buffer under a predetermined condition.
At step 240, the data area is programmed when the inputted program command is the command for programming the data area in step 220. That is, data inputted through a page buffer is programmed into a designated page of a cell array. At step 230, when the inputted program command is the command for programming the FAT block in step 220, data is inverted and inputted into the page buffer. At step 250, the inverted data is programmed into the FAT area. As described above, “0” in the FAT area indicates that no data are written, that is, the FAT area is in an erase state. Therefore, an erase operation is first performed on a previous block whenever data is inputted. According to the present embodiment, the inversion of the incoming data makes it unnecessary to perform the erase operation on the previous block. Meanwhile, the data is inverted before data output even in the read operation. Therefore, upon programming the FAT block, the corresponding information is separately stored in a flag cell. When a read operation is performed on the FAT block according to the corresponding information, the data is inverted again before its output. In this way, the information indicating that the program operation has been performed on the FAT block can be stored in a flag cell. That is, upon programming the FAT block, the flag cell is also programmed. Thereafter, when a read command is received, it is determined whether or not the flag cell has been programmed. If the flag cell is in a programmed state, the read command is deemed to be related to a read operation on the FAT block. As a result, the data is inverted and then outputted. On the other hand, if it is determined that the flag cell is in a non-programmed state, the read command is deemed to be related to a read operation on the data area. Thus, the data is outputted without inversion.
The main cell array 410 includes a plurality of cell strings 411. Each of the cell strings 411 includes select transistors and memory cells connected in series. Each of the cell strings 411 is connected to a corresponding bit line 412 and is connected to the main page buffer 430 through the bit line 412. The bit line 412 includes an even bit line BLe and an odd bit line BLo in the present implementation. A pair of the even bit line BLe and the odd bit line BLo is connected to a single page buffer of the main page buffer 430. The flag cell array 420 has a similar cell string structure as the main cell array 410.
The main page buffer 430 includes a selecting/biasing unit 431, a precharging unit 432, and a latching unit 433. The selecting/biasing unit 431 selects one of the even bit line BLe and the odd bit line BLo and applies a bias voltage to the bit line 412. The precharging unit 432 precharges the bit line 412. The latching unit 433 latches data. The selecting/biasing unit 431, the precharging unit 432, and the latching unit 433 are connected through a sensing node S. The latching unit 433 is connected to an output node Q. The data inverter 450 is connected to the output node Q through first and second data input/output (I/O) lines 434 and 435. The first data I/O line 434 is switched by a transistor 436, and the second data I/O line 435 is connected to an inverter 438. Therefore, data is inverted through the second data I/O line 435.
The flag cell page buffer 440 has a similar configuration as the main page buffer 430. One difference is that a flag control signal unit 441 and a path control unit 442 are further provided. The flag control signal unit 441 determines the state of an output node (Q) of the flag cell page buffer 440 according to a flag control signal FLAG_MRST. The flag control signal FLAG_MRST is in a high state to program the FAT block, and is in a low state to program the data area. The path control unit 442 controls a data transfer path within the main page buffer 430 according to whether the flag cell 420 has been programmed. To this end, the path control unit 442 includes a first switch 442 a and a second switch 442 b. The first switch 442 a is an n-channel MOS transistor and the second switch 442 b is a p-channel MOS transistor. A control signal PGMb is commonly inputted to gates of the first and second switches 442 a and 442 b. The first switch 442 a has a drain connected to the output node Q and a source connected to a node A. The second switch 442 b has a drain receiving a control signal PGM and a source connected to the node A. The node A is connected to a first control line 443 and a second control line 444. The first and second control lines 443 and 444 control transistors 436 and 437 of the main page buffer 430. An inverter 445 is disposed on the first control line 443 to invert a state of the node A.
The data inverter 450 is connected to the main page buffer 430. The data inverter 450 includes a data input line 454 extending from the I/O line of the main page buffer 430. In addition, the data inverter 450 further includes a transistor 451, an inverter 452, and a data inversion input line 453. The transistor 451 is controlled by the flag control signal FLAG_MRST, and the inverter 452 is serially connected to the transistor 451. The data inversion input line 453 is connected to the inverter 452. When inputting data for program, if the flag control signal FLAG_MRST is in a high state, an input data is inverted by the inverter 452 and outputted through the data inversion input line 453. On the other hand, if the flag control signal FLAG_MRST is in a low state, data is transferred through the data input line 454 without inversion.
In programming the FAT block, the program control signal PGM of a logic high level and the flag control signal FLAG_MRST of a logic high level are applied. Thus, the transistor 451 of the data inverter 450 is turned on so that the inverted data is inputted through the data inversion input line 453. Since the flag control signal FLAG_MRST is in the high state, the output node Q of the flag cell page buffer 440 becomes a low state, but the node A becomes a high state due to the operation of the path control unit 442. Since the node A is in the high state, the transistor 436 of the main page buffer 430 is turned on. As indicated by an arrow 520, the inverted data is inputted through the inversion input line 453 of the data inverter 450 and the first data I/O line 434 of the main page buffer 430. The program operation is performed on the main cell array 410 in units of pages according to the inverted data. Since the flag control signal FLAG_MRST of the logic high level is applied, the output node Q of the flag cell page buffer 440 becomes a low state and the flag cell 420 corresponding to the programmed page of the FAT block is programmed. In this way, since the inverted data is inputted in programming the FAT area, the data can be added to the FAT area by programming only the added data, without performing the erase operation on the overall FAT block.
In adding the data to the FAT area having the programmed state and the erased state the same as those of the data area, only the added data can be programmed without performing the erase operation by blocks, thereby improving the E/W cycling characteristic. Further, the data can be updated in the FAT area without performing the erase operation, thereby increasing the data update speed of the FAT area.
While the present invention has been described with respect to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.
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|U.S. Classification||365/230.03, 711/103, 365/185.33, 365/189.011|
|Cooperative Classification||G11C16/10, G06F12/0246, G11C11/5628, G11C2211/5647, G06F2212/1036, G06F2212/7207|
|European Classification||G06F12/02D2E2, G11C16/10, G11C11/56D2|
|Jan 3, 2011||AS||Assignment|
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:JOO, SEOK JIN;REEL/FRAME:025571/0830
Effective date: 20071213
Owner name: HYNIX SEMICONDUCTOR INC., KOREA, REPUBLIC OF
|Jun 15, 2014||FPAY||Fee payment|
Year of fee payment: 4